Thursday, November 12, 2009

Important note: if you have a question to ask, please ask it at Lawn Mower Forum, either in the Black & Decker area or the Electric & Battery Operated area at that website. I apologize for being unable to handle individual requests for help posted on this blog or sent by email.

The Story

Last spring, my CMM1000 mower developed a problem where it would simply stop running after 5 or 10 minutes. It would restart again after a minute, but then only run a few minutes before stopping again.

The problem turned out to be a faulty circuit breaker, which is supposed to cut the motor off when the current exceeds 40 Amps but was actually tripping at a lower current. At first I misdiagnosed the problem as either a worn out battery or bad switch contacts. At a loss as to what the cause was, an internet search led me to other people with the same problem ... and more importantly to somebody who had fixed it by replacing the breaker. And so I extend a hearty thank you to "rothompsons", whoever you are, for posting the solution at forums2.gardenweb.com.
After ordering a new breaker for $19 ($12 part + $7 shipping) from ereplacementparts.com, the mower was up and running again! In the intervening month it took to find and fix the problem, I used our trusty manual push-reel mower to cut our grass.

By the way, my original breaker lasted 3 years, and rothompsons's lasted 2-1/2. Another person did report that their mower was 6 years old when they first encountered the problem. At any rate, you can expect your breaker to fail eventually. You'll know it's the breaker if your mower stops, and can be restarted only after you hear a "click" about 30-60 seconds later. The click is the automatic reset switch inside the breaker, after it has cooled down enogh to close the circuit again.

Repair details

If you need to replace your circuit breaker, here is where you can find it on the mower's Main Circuit Board:

Main circuit board, showing location of circuit breaker.

The breaker is in series with the main switch, and when tripped breaks the connection from the battery to the motor. It is attached to the main circuit board using nylon-insert lock nuts:

A view of the brand new circuit breaker, part # 5140004-81 from ereplacementparts.com:

The brand new circuit breaker (includes nuts and lockwashers) from ereplacementparts.com

Request of readers:

And finally, here is a request of anyone reading this blog. If you can find these circuit breakers for cheaper than the $12 I paid for this one, I would love to hear about it! Please note, it is manufactured by Cooper Bussman, and is their Shortstop series 120 circuit breaker. It should be rated for:

24 V

40 A

Must be of the automatic reset, thermal cycling type, not the manual rest type.

I have found a 12V version for under $4 at www.wiringproducts.com, but so far not a 24V version. It would be nice to order a few of these to have in stock.

[Added May 2011:]
As of spring 2011, I'm finding some parts discontinued at ereplacementparts. An alternative, though incomplete, supplier is abtecparts.comThanks to Ajay for telling us about abtecparts.